1) Field of the Invention
The present invention relates to a process for producing an aqueous high concentration coal slurry. More particularly, the present invention relates to a process for producing an aqueous high concentration coal slurry having an excellent stability during storage and transportation.
2) Description of the Related Arts
Recently, the importance of coal as an energy source has been revalued, but coal is disadvantageous in that it is a solid material and thus is difficult to transport, store and handle, in comparison with oil.
Accordingly, many attempts have been made to eliminate the above-mentioned disadvantages by finely pulverizing a coal material, dispersing the resultant fine coal particles in an aqueous medium to provide an aqueous coal slurry which can be stored, transported and handled as a liquid material, and supplying the aqueous coal slurry as a fuel for boilers for power plants and other industrial uses. For example, such attempts are disclosed in Japanese Unexamined Patent Publication (Kokai) Nos. 58-38791, 60-18585, 61-57689 and 62-116691.
For the aqueous coal slurry, it is necessary to increase the concentration of coal particles and to enhance the stability in transportation and storage. A high concentration aqueous coal slurry should comprise 60% to 75% by weight of finely pulverized coal particles and 25% to 40% of an aqueous medium containing a small amount of an additive, for example, a dispersing agent, and this high concentration of coal particles can be obtained by adjusting the size of the coal particles in the aqueous slurry to a suitable level and distribution thereof, and by adding an appropriate additive to the aqueous slurry.
Therefore, attempts have been made to provide a method of controlling the distribution of the size of the coal particles in the aqueous slurry in accordance with an optimum particle size distribution formula. Those attempts, however, are not always satisfactory. Also, the conventional methods are disadvantageous in that the high concentration of coal particles in the aqueous slurry can be realized only by adding a relatively large amount of a dispersing agent to the aqueous medium.